Automated handling system have been developed for use in mail handling, manufacturing, warehouse operations, and other applications. Generally, these systems have been adapted for transporting articles between various fixed locations such as between workstations, physical storage locations, and article loading and unloading stations. Accordingly, many of these systems are provided with a fixed pathway that is disposed between the stations for guiding the motion of one or more automatic article carriers. These systems are therefore disadvantageous when modifications need to be made to the processing plant in which they are implemented. Adding to or rerouting the pathway to accommodate the installation of new equipment and the rearrangement or removal of existing equipment is difficult because such adaptation generally requires significant changes in the control system for carrier operation along the pathway.
Some article handling systems comprise a central storage facility for articles being transported within the handling system. The storage facility generally comprises a grid of individual compartments which are each identifiable by a unique address and provided with sensors for detecting the presence of an article stored therein. A processor controls the operation of at least one vehicle to store and retrieve articles to and from selected compartments using shelf address and sensor data. Centralized storage, however, is disadvantageous in most article handling applications because the distance between workstations and the central storage area is long, thereby contributing to longer article carrier transit times and reduced system throughput.
Various systems have been proposed for controlling article carrier motion in article handling systems. For example, a first system provides carriers, which are confined to travel along a rail, with control signals that are transmitted along conductors within the rails. This type of carrier control system is disadvantageous because a failure in the rail conductors can result in the termination of control signal transmission and, therefore, the complete failure of the control system. A second system provides carriers with transceivers for receiving control signals from a transmitter located along the carrier path. This type of carrier control system is restricted to those areas of operation that are within the communication range of the transmitter. With either type of carrier control system, expansion of the article handling system is difficult because the addition of rails or carriers can require extensive modification of the existing control system and sometimes costly redesign and coordination with new control system components.